Set in an alternate steampunk past, an Austrian fugitive prince and a Scottish airman in disguise embark on an unexpected quest to prevent a world war.

The series follows John Porter, a former British Special Forces soldier, who is drafted back into service by Section 20, a fictional branch of the Secret Intelligence Service.

Kidnapped as children and conscripted into a brutal military training and augmentation program, the Spartans were designed to be the ultimate weapon against chaos and insurgency—but when a dangerous alien alliance known as the Covenant declares war on humanity, the Spartans might be our only hope.